Deep Drawing Tests Research Articles

Stamping Formability of ZE10 Magnesium Alloy Sheets

Abstract ZE10 magnesium alloy sheets were prepared through ingot casting and the hot-rolling process. The mechanical properties, conical cup value ( CCV), bore expanding performance, and limit drawing ratio ( LDR) were investigated to examine the stamping formability of ZE10 alloy sheets, at temperatures ranging from 20 to 300 °C. The results showed that the tensile strength decreased, whereas, plasticity, drawing-bulging performance, bore expanding properties, and deep drawing performance increased markedly at elevated temperatures. The CCV specimens could be drawn into the conical die's underside cylindrical hole from the conical cliff, without cracking, and could have the minimum CCV at 200 and 250 °C. In the bore-expanding test, the bore (Φ10 mm) could be expanded to the dimension of the punch (Φ25 mm) and the maximum bore-expanding ratio could be achieved at above 150 °C. The limiting drawing ratio ( LDR) of 2.85 is acquired during the deep drawing test at 230 °C. with the punch temperature of 20 ∼ 50 °C, the punch velocity of 50 mm · min −1, and the mixture of graphite and cylinder grease as lubricant.

Investigations on the Mechanical Properties and Formability of Friction Stir Welded Tailored Blanks

Tight competition characterizing automotive industries in the last decades has determined a strong research effort aimed to improve utilized processes and materials in sheet stamping. As far as the latter are regarded light weight alloys, high strength steels and tailored blanks have been increasingly utilized with the aim to reduce parts weight and fuel consumptions. In the paper the mechanical properties and formability of tailored welded blanks made of a precipitation hardenable aluminum alloy but with different sheet thicknesses, have been investigated: both laser welding and friction stir welding have been developed to obtain the tailored blanks. For both welding operations a wide range of the thickness ratios has been considered. The formability of the obtained blanks has been characterized through tensile tests and cup deep drawing tests, in order to show the formability in dependency of the stress condition; what is more mechanical and metallurgical investigations have been made on the welded joints.

Evaluation of stamping lubricants using the deep drawing test

This paper presents a practical methodology that uses the deep drawing test and finite element (FE) analysis to evaluate stamping lubricants under near production conditions. In stamping operations good lubrication helps to reduce wrinkling, premature fracture, and localized thinning. Furthermore, lubrication also reduces tool wear in large-volume production. Determination of reliable friction data associated with a given lubrication system is also important for successful process design and simulation by FE analysis. In this study, five stamping lubricants (four dry film lubes and one wet lube) were evaluated using the deep drawing test. The performance of the lubricants were evaluated based on: (a) maximum punch force measured, (b) the maximum applicable blank holder force (BHF), (c) the draw-in length, (d) the perimeter of flange after test, (e) the change of surface roughness, and (f) the inspection of surface topography. The coefficient of friction for each lubricant tested was determined through the FE-based inverse analysis by matching the predicted and measured values of the load-stroke curve and the draw-in length. This study showed that one of the tested lubricants was most effective, regardless of test speed and the magnitude of BHF. The methodology used was shown to be effective in evaluating various lubricants for sheet metal forming and accurately differentiating their performances.

Feasibility study of twin roll casting process for magnesium alloys

Abstract This paper is concerned with the development of a strip casting technology for manufacturing magnesium alloy sheets. The aim of the work is to establish a manufacturing process and technology to facilitate the economical manufacture of high-quality magnesium alloy sheets. Magnesium alloy AZ31, AZ61, AM60 and AZ91 were used to investigate the appropriate manufacturing conditions for use in twin roll strip casting. Temperatures of the molten materials and roll speeds were varied to find the appropriate manufacturing conditions. The effects of manufacturing conditions on possible forming were clarified in terms of roll speeds and roll gaps between upper and lower rolls. In addition, microscopic observation of the microstructure of the finished casting was performed. It was clarified that a magnesium sheet of 2.5–4.5 mm thickness could be produced at a speed of 20 m/min by a horizontal copper roll caster. Mill stiffness and a method of predicting the cast sheet's thickness were investigated to determine the appropriate manufacturing conditions. It was also found that the cast magnesium sheet of AZ31, AZ61, AM60 and AZ91 manufactured by roll strip casting could be used for plastic forming if the appropriate magnesium sheets were produced after the roll casting process. By a warm deep-drawing test, it also demonstrated that a limiting drawing ratio of 2.4 was possible in the case of AZ91 sheet that was difficult to be manufactured by conventional extrusion process or DC casting and hot-rolling process for magesium alloy sheets with high aluminium contents.

AZ3l 판재의 온간 사각컵 디프드로잉에서 금형 설계에 대한 성형성 민감도의 평가

Magnesium alloy has low formability at room temperature and therefore, in many cases, forming at elevated temperatures is necessary to obtain the required material flow without failure. Tn the present study, square cup deep drawing tests using the magnesium alloy AE31 sheet were experimentally conducted using the porches and dies with different edge radius to evaluate the formability sensitivity to the die design variables. The experimental results showed that the fracture position over the cup wall moved from the punch nose to the flange as the die temperature increased, and that the drawing depth change was more affected by the punch radius than the die radius.

Effect of alternating blank holder motion of drawing and wrinkle elimination on deep-drawability

The effect of controlling blank holder motion by a newly proposed algorithm on deep-drawability was investigated for a circular-cup deep-drawing process of a thin sheet metal, from the perspective of wrinkle behavior as well as the fracture limit. The algorithm for controlling blank holder motion, such that blank holder force is extremely low, by temporarily allowing wrinkling has been proposed by the authors for improving the deep-drawability of thin blanks. Experimental deep drawing tests of a Cu alloy sheet were carried out to evaluate the effect of motion control on wrinkle behavior. Finite element (FE) simulations of the deep drawing process were also conducted to investigate the effect of the method on fracture damage reduction. In the previous work by FE simulation, we showed that the motion control method is effective for forming relatively thin sheet blanks, and that the performance of the control method significantly depends on control parameters, i.e., minimum and maximum allowable wrinkle heights, which are associated with wrinkle recognition. The results of the experiment indicated that wrinkle elimination can be successful if wrinkles are within the allowable height range. FE simulation results also indicated that deep-drawability can be improved as a result of the reduction of ductile damage accumulation when using blank holder control.

나노인덴테이션 시험과 유한요소해석을 이용한 자동차 도금 강판의 도금층 체적 거동결정 및 성형해석 적용

Coating layers on a coated sheet steel frequently affect distributions of strain rate of sheets and deteriorate the frictional characteristics between sheets and tools in sheet metal forming. Thus, it is important to identify the deformation behavior of these coatings to ensure the success of the sheet forming operation. In this study, the technique using nano-indentation test, FE-simulation and Artificial Neural Network(ANN) were proposed to determine the power law stress-strain behavior of coating layer and the power law behavior of extracted coating layers was examined using FE-simulation of drawing and nano-indentation process. Also, deep drawing test was performed to estimate the formability and frictional characteristic of coated sheet, which was calculated using the linear relationship between drawing force and blank holding force obtained from the deep drawing test. FE-simulations of the drawing process were respectively carried out for single-behavior FEmodel having one stress-strain behavior and for layer-behavior FE-model which consist of coating and substrate separately. The results of simulations showed that layer-behavior model can predict drawing forces with more accuracy in comparison with single-behavior model. Also, mean friction coefficients used in FEsimulation signify the value that can occur maximum drawing force in a drawing test.

Fracture in sheet metal forming: Effect of ductile damage evolution

This work deals with the virtual simulation of the sheet metal stamping process. The main objective is to predict when and where the cracks can appear in the workpiece during the forming operation. A local approach based on the strong coupling between anisotropic elastoplasticity with mixed nonlinear work hardening (isotropic and kinematic) and an isotropic ductile damage is proposed. The theoretical and numerical aspects of the constitutive equations are, first, presented. The resolution of the resulting system of equations is carried out via a Vumat user material, using ABAQUS/Explicit finite element code. The results obtained, in the context of Swift’s benchmark deep-drawing test show the efficiency and the potential interest of the proposed damage model.

Residual Stress State at Different Scales in Deep Drawn Cup of Unstable Austenitic Steel

In this study, residual stresses state at different scales in the 301LN unstable austenitic steel after deep drawing was determined. The first part of the work deals with the characterization of the martensitic transformation during uniaxial loading. The austenite/martensite content which was determined by X-Ray Diffraction increases until a maximum of 0.6 for 30% strain. Internal stress distribution was determined by coupling in-situ tensile tests with sin²ψ method. As soon as martensite appears, the magnitudes of the internal stresses in this phase were found to be 400 MPa higher than in the austenite. To establish a relation between the complex loading path effect and the phase stress state, deep drawing tests were carried out for different drawing ratios. Both macroscopic tangential residual stresses and residual stresses in the martensite were determined. It appears that the macroscopic tangential residual stresses are positive and increase with increasing drawing ratios and the maximum value is located at middle height of the cup. It is about 850MPa for the Drawing Ratio (DR)=2.00. The tangential residual stresses in the martensite were found to be positive in the external face and have a same evolution as the macroscopic ones.

Warm deep drawing of wrought magnesium alloy sheets produced by semi-solid roll strip-casting process

This paper is concerned with the development of a continuous strip-casting technology to facilitate the manufacture of magnesium sheet alloys economically whilst maintaining high quality. Established in the paper is warm formability of cast magnesium alloy sheets after being hot rolled by semi-solid roll strip-casting process. It has been found that magnesium sheet with 2.0–4.0 mm thickness could be produced at a speed of 25 m/min. Hot rolling and annealing temperatures during hot rolling were also changed to examine which condition would be appropriate for producing wrought magnesium alloys with good formability. Microstructures of the crystals of the manufactured wrought magnesium alloys were observed. It has been found that a limiting drawing ratio of 2.7 was possible in a warm deep-drawing test of the cast magnesium alloy sheets after being hot rolled.

마그네슘 합금 AZ31 판재의 온간 사각컵 디프드로잉 공정의 유한요소 해석

Magnesium alloys are expected to be widely used fur the parts of structural and electronic appliances due to their lightweight and EMI shielding characteristics. While the die casting has been mainly used to manufacture the parts from the magnesium alloys, the press forming is considered as an alternative to the die casting for saving the manufacturing cost and improving the structural strength of the magnesium alloy parts. However, the magnesium alloy has low formability at room temperature and therefore, in many cases, forming at elevated temperatures is necessary to obtain the required material flow without failure. In the present study, square cup deep drawing tests using the magnesium alloy AZ31 sheet were experimentally conducted at various elevated temperatures as well as room temperature, and the corresponding finite-element simulations, which calculated the damage evolution based on the Oyane's criterion, were conducted using the stress-strain relations from the tensile tests at various temperatures. The formability predictability by the finite-element analysis was investigated by comparing the predicted damage distributions over the deformed AZ31 sheet at elevated temperatures with the corresponding experimental deformations with failures.

Ｍｇ‐２．０〜４．５％Ａｌ‐０．７〜１．５％Ｚｎ合金の高温変形特性と成形性

Mg-Al-Zn alloys containing 2.0-4.5%Al and 0.7-1.5% Zn were cast and subsequently hot-rolled, and then the rolled sheets having a thickness of 0.83 mm were prepared. After that, they were annealed at 498 K and 623 K for 1 h. The deformation characteristics and formabilities of as-rolled (F) and annealed sheets are investigated in terms of metallography. In tensile test at 498 K fine recrystallized grains enhance grain boundary sliding, which contributes to deformation in direction of sheet thickness, in specimens with higher Al and Zn contents, resulting in isotropic deformation behavior. Deep drawing tests at 498 K reveals that the deep drawability is improved with increasing Al and Zn contents up to Al content of 3% because more dynamic recrystallized grains are generated during forming. As a result, limiting drawing ratio (LDR) of Mg-3%Al-1%Zn reaches 3.2. Excessive Al and Zn contents generate numerous fine recrystallized grains, which give rise to significant grain boundary sliding, resulting in large reduction in thickness. Therefore, LDR of Mg-4.5%Al-1.5%Zn decrease to 2.8. However, this LDR is much higher than those of aluminum alloys and steel, indicating enough formability can be obtained even in the high strength magnesium alloy. The F-specimens containing large residual working strain exhibit higher formability than the annealed specimens as a result of dynamic recrystallization during forming. Also in the stretch forming utilizing hemispherical punch with the diameter of 40 mm, the F-specimens show excellent stretch formability. That is, limiting dome height of the alloys containing Al more than 3% reaches 15 mm.

2751 マグネシウム合金の深絞り特性に関する研究(S29-2 アルミニウム合金およびマグネシウム合金の創製と加工技術(2),S29 アルミニウム合金およびマグネシウム合金の創製と加工技術)

The deep drawing test in magnesium alloy sheet AZ31 was executed and the authors discussed the effect of the test conditions (temperature, lubricant, blank holding pressure and processing speed, etc.) on the formability. As a result, we obtained as follows: (1) In the case of lubricant CF-853 added with the Teflon powder, the good states of deep drawing was obtained. (2) A blank holding load of 8OkN was found as a good value to prevent the flange wrinkle. (3) 1mm thickness AZ31 sheets shows poor formability less than 160℃ and shows the good formability at 200℃ for any speed.

エンボス・リストレーション加工によるアルミニウム合金板の成形性向上

Using thinner sheet metal is effective in making the products with low cost and light weight. It also contributes to saving the energy and resources on earth. However, the rigidity and formability of sheet metal decrease when the thickness of sheet becomes thinner. Emboss process and restoration process can locally change the shape of a sheet metal, and also add partial work hardening. Therefore, there are some possibilities that the formability of thinner sheet metal is improved by these processing, like as the rigidity. In this study, emboss processes and restoration processes were conducted to the aluminum alloy sheet. The variations of the strength and formability of the aluminum sheet by these processing were investigated. The results showed that the yield stress of the sheet changed and the total elongation increased by performing these processing. On the basis of these results, the improvement of the formability of sheet metal was attempted by emboss process, restoration process and combination of these. The Erichsen cupping test and the deep-drawing test were conducted to the sheets having some processing patterns. From the result, it was confirmed that it was possible to improve the formability of sheet metal by adopting emboss process and restoration process properly.

Texture, Tensile Properties and Press Formability of Mg-3Al-1Zn/Ti Clad Sheets Produced by Roll-Bonding

In order to improve corrosion resistance and mechanical properties of magnesium alloys, titanium with high specific strength was warm roll-bonded on the surface of AZ31 magnesium alloy sheets. Although the AZ31 alloy before roll-bonding had a typical basal texture, the AZ31 layer that constitutes a larger part of the clad sheet clearly showed off-basal texture with c-axis inclined by about 10º from the normal direction toward the rolling direction. This texture significantly affected tensile properties of clad sheets, resulting in lower proof stress and higher elongation at the rolling direction than at the transverse direction. In deep drawing tests, the 2-layered clad sheet with an outer titanium layer could be successfully formed at temperatures considerably lower than the limiting forming temperature of an original AZ31 single sheet. This is probably due to an effect of the outer titanium layer bearing tensile stress at a shoulder part of cup and an additional effect of improved deformability by off-basal texture in the AZ31 layer.

Carbon based tool coatings as an approach for environmentally friendly metal forming processes

The deep-drawing of austenitic stainless steel AISI 304 provides a considerable challenge for production engineers. A major problem in such processes is adhesive tool wear which is often prevented using chlorous mineral oils. The aim of this work was to replace these hazardous lubricants with biodegradable, rape oil based fluids. For that purpose a modified triglyceride named HIGTO(I) is used in combination with a graded zirconium carbide (ZrC g) physical vapour deposition (PVD) tool coating chosen because of their good performance in previous studies. The results from deep-drawing tests with uncoated dies show that HIGTO(I) itself is not able to replace chlorous deep-drawing oils. But in combination with HIGTO(I) as a lubricant and ZrC g as tool coating deep-drawing forces are reduced and adhesive tool wear is prevented. This combination even exceeds the performance of chlorous deep-drawing oils. The wear effects, which appeared in different tests, could be explained by an analysis of tool loads and process temperatures, calculated using FE-simulations.

Flexibly Rolled Sheet Metal and Its Use in Sheet Metal Forming

Light weight construction is a construction philosophy which aims at maximum weight reduction. Reasons for light weight construction can be very diverse. One main cause can be to improve fuel efficiency. This can be achieved by use of load optimised sheet thicknesses. Another reason can be the increasing demands on crash performances by optimisation of local properties. This paper presents two production processes of flexibly rolled blanks, one with longitudinal and the other one with latitudinal thickness transitions. Both of them have been developed at the Institute of Metal Forming (IBF) and yet found their way into series production. The potential of these processes is already proved by a large range of products, especially in automotive industries. Some special deep drawing tests with flexibly rolled blanks have been conducted and their results are presented. Also process simulation has been carried out at the IBF and will be explained. One possibility with regard to optimise these products is shortly introduced. Completing this paper an outlook is given.

Correlation Between the Microstructure of Galvannealed Coatings and the Defoliation during Press Forming

Abstract The defoliation properties of galvannealed coating, so-called powdering and flaking, in continuous galvanizing line were investigated by scanning electron microscopy, X-ray diffraction, roughness profiler and deep drawing test. Both aluminum content in molten zinc and galvannealing temperature were turned out to be critical factors on the microstructure and mechanical properties of galvannealed coatings. Below 0.135 wt% Al, coating surface composed of the mixture of granular d1p and columnar z phases. While, above 0.155 wt% Al, coating surface contained the mixture of granular d1p and pan-cake d1k phases. The appearance of brittle d1k phase approximately 10 μm in size can account for the high amount of defoliation during deep drawing test. The formation of relatively ductile z phase and thin G phase contributes to improve the press formability. The optimazation of the surface microstructure controlling the ratio of granular d1p and columnar z phases was important to reduce the powdering.

Deep Drawing of Friction Stir Welded Thin Sheet Aluminium Steel Tailored Hybrids

Friction stir welding undergoes a steep evolution in industrial applications since the invention in the early 1990s. Especially for aluminium alloys in sheet thicknesses over 2 mm a lot of applications are established, whereas a lack in knowledge about friction stir welding of thin sheets with sheet thickness less than 2 mm exists. This article deals with friction stir welding of thin sheet aluminium steel tailored hybrids and their formability. These investigations tend to close the gap of availability of friction stir welded blanks in the range of 1 mm sheet thickness and to offer new applications of this joining technology. For production of aluminium steel tailored hybrids AA5182 with a thickness of 1.2 mm and DC04 in 1.0 mm are used, the joining partners are friction stir welded in a lap joint. Different tool geometries and process parameters are performed to achieve the highest strength and elongation at fracture of the tailored hybrids. The influence of the stirring on the arrangement and distribution of both materials in the welding zone and its microstructure is analysed using light optical and scanning electron microscopy. In addition to tensile tests planar microhardness measurements help to detect the local changes of the mechanical properties in the characteristic zones of the weld seam. Tailored hybrids, which were friction stir welded with the best welding parameters in accordance to the mechanical properties of the weld seams, were used for deep drawing tests of friction stir welded thin sheet aluminium steel tailored hybrids. The maximum drawing ratio of these tailored hybrids coincides with the one of the parent material of AA5182.

Effects of Rolling Condition on Warm Deep Drawability of Magnesium Alloy Sheets Produced by Twin-Roll Strip Casting

Effects of rolling conditions on warm deep drawability of cast magnesium alloy that were hot rolled after roll strip casting were investigated to ascertain the feasibility of twin-roll strip casting process of AZ31B magnesium alloy. Hot rolling and heat treatment conditions were changed to examine which conditions were appropriate for producing AZ31B wrought magnesium alloys after strip casting process. Microscopic observation of the crystals of the manufactured wrought magnesium alloys was performed. It has been found that a limiting drawing ratio of 2.7 was possible in a warm deep drawing test of the cast magnesium alloy sheets after being hot rolled.